1. Field of the Invention
The present invention generally relates to semiconductor laser devices and, more particularly, is directed to the structure of a semiconductor laser package having a semiconductor laser element.
2. Description of the Prior
The semiconductor laser is required to be cooled more effectively according to the increase of the output power thereof.
As one of the methods for cooling the semiconductor laser effectively, there has been proposed to employ elements in the Peltier effect (herein after referred to as Peltier elements) which are capable of being utilized as thermoelectric cooling elements.
One example of this method will be explained with reference to FIG. 1 illustrating the cross section of the conventional semiconductor laser package. Referring to FIG. 1, Peltier elements, that is, a Peltier element group 53 is sandwiched a lower substrate 51 and an upper substrate 52 each deposited with such a conductive pattern in which one electrode of each Peltier element is connected thereto to connect, for example, adjacent Peltier elements sequentially. Thus, a cooling structure 54, that is, a thermoelectric (TE) cooler constituted by the Peltier element group 53, lower substrate 51 and upper substrate 52 which serves as a cooling electrode side or a heat absorption electrode side. A heat sink 56 provided with a semiconductor laser element 55 is mounted on the upper substrate 52. A photo detecting element such as a photo diode 57 is mounted on the upper substrate 52 such that the photo diode 57 detects the laser beam emitted from the rear side of the laser element 55 to thereby control the laser element 55 so that it is held to a predetermined operating state.
The cooling structure 54 mounted with the laser element 55 in this manner is mounted on a base member 59 of a semiconductor laser package 58, for example, a metal casing or the like such that its lower substrate 51 is jointed to the base member 59 through solder 60.
A plurality of lead wires 61 are hermetically lead out from the package 58 so as to lead out wires of the Peltier element group 53, laser element 55 and optical detection element 57 or the like. A cap member 63 having a light transmission window 62 for conducting the laser beam from the laser element 55 is attached on the top end of the package 58 to hermetically seal the cooling structure 54 within the package 58.
The package 58, if necessary, may be mounted on a cooling member having radiator fins or a water cooler or the like such that the base member 59 thereof is thermally coupled thereto so as to emit radiant energy from a heated electrode side or a heat generation side of the Peltier element group.
According to this prior-art semiconductor laser package, however, since the lower substrate 51 of the cooling structure 54, that is, the heated electrode side is soldered to the base member 59, the thermal transmission from the heated electrode side to the base member is degraded remarkably. Thus, the laser element may not be cooled sufficiently, resulting in the increase of the temperature of the laser element, which prevents the stable oscillation thereof or misleads the oscillation wavelength. Accordingly, this prior-art semiconductor laser package has the disadvantage such that, when applied to the excitation of a solid state laser such as a YAG laser, the excitation efficiency is degraded.
Further, the prior-art semiconductor laser package has the disadvantage such that, when constructing it, the soldering processing of the lower substrate 51 of the cooling member 54 and also the soldering processing of the lead wires for leading the wires out of the package 58 must be performed at the narrow area within the package 58, thereby degrading the productivity remarkably and increasing the cost.